Police and gendarmerie statistics show a rise in violent acts committed by French teenagers between 1993 and 2008. In the same period, the consumption of psychoactive substances increased, fuelling the debate on the role of drugs in violent acts committed and recorded. But the causes of violent behaviour are, of course, diverse-ranging from social origin to personal and family problems and other factors. This study seeks to compile an inventory of violent acts reported by French adolescents-including acts committed or suffered-and then to test factors that can be linked to such acts: the use of psychoactive substances, and the characteristics of the person's social background (such as family structure and the parents' socio-occupational category). The data and results are based on a survey covering a representative sample of young French males aged 17. The survey is conducted periodically on the occasion of “Defence Preparation Day” (Journée d'Appel de Préparation à la Défense: JAPD), instituted in 1998 after the abolition of national service. The findings show that youths from modest backgrounds are more likely than others to state that they engage in violent behaviour (taking part in fights, using a weapon, or causing injuries requiring medical assistance). This gap is wider for youths who report that they are very seldom victims of verbal or physical violence (threats, assault or injuries requiring medical assistance) or of theft. The social-origin gap is much smaller for youths having suffered a larger number of violent acts. A final set of factors influencing violent behaviour consists of family structure, degree of good relations in the family, depression, and drug use.